MGS4 isn't on it's own but marry this with recent release of GTA4, 80GB PS3 and other info like release date for LBP - the PS3 is looking like an attractive package all of a sudden.
There just may have been a lot of savvy people waiting for the 80GB that may have been sold on the PS3 when GTA4 got released. I reckon the PS3 will do just fine when MGS4 gets released.